| Jointed factors of broken topgraph, less and concentrated rain, single soil type as well as inappropriate agricultural techniques lead to serious soil and water loss in the rolling and gullied area of Loess Plateau, which make further deterioration of ecological environment, continued declining of soil fertility, low and unstable crop yields, increasing of production costs year after year. Therefore, it is essential to develop agricultural techniques which can reduce soil and water loss in this area. In order to exploring soil management technology system of water storage and conservation which is suitable for this area, improving utilization efficiency of natural precipitation and soil moisture, providing a basis for agricultural techniques of soil and water conservation and establishing a development direction of this area, the author of this thesis took represented Mizhi county of Shaanxi province as study area, has finished systematic researches on the temporal and spatial variation of soil moisture characteristics, soil water consumption law, crop yield and water use efficiency under 5 agricultural techniques including no-crop of no-tillage, straw mulch of no-tillage, combination coverage, plastic film coverage and so on, using integrated evaluation method, confirmed the applicated prospect of "double material coverage combined with groove and ridge "measures in this area. The main findings are as follows:(1) The results in different agro-technical measures for temporal and spatial variation of soil moisture show that seasonal dynamics of soil moisture of no-tillage no-crop measures in normal years can be divided into four stages relatively: increasing moisture slowly in spring, stable moisture relativly in spring and summer, losing moisture slowly in summer and autumn, fast lose moisture in winter and spring. soil moisture profile can be divided into four layers: rapid change layer of soil moisture (0~10cm), active layer of soil moisture (10~40cm), sub-active layer of soil moisture (40~140cm) and relatively stable layer of soil moisture (140~200cm). Different agro-technical measures in the drought year, usual year and wet year, the upper and lower soil moisture change in seasonal trends have their own characteristics, dynamics of soil moisture of no-tillage measures are more consistent in drought year, and film coverage measures in normal year. But, the combined coverage measures in normal year changed in upper and lower soil moisture has shown a distinct changable trend, no-tillage straw mulch measures in wet-year changed in upper and lower soil moisture has more consistent trends. Whether dry years or wet years, 60cm layer of soil is the most active layer of soil moisture, as well as the exchange interface of soil water between upper and lower soil layer; 120cm layer is a clear lower water line in crop land. The impact depth on soil moisture of ground management measures is at the range of 0~60cm. Different agro-technical measures in dry years, temporal and spatial variation of soil moisture can be described as a binary quadratic regression equation Y = a + bX1 + cX2 + dX12 + eX22 + fX1X2, but different management measures vary greatly between the regression coefficients. At the same time, the soil moisture contour map that draw by computer technology, which for conventional tillage (CT), straw mulch with no-tillage (MF) and bare land with no-tillage (CK) in dry years, can also better reflect the change trend of soil moisture temporal and spatial variation, this result is the same as the numerical analysis and regression analysis findings aforementioned.(2) The research results of soil evaporation characteristics in different agro-technical measures show that, evaporation of bare soil in the loess hilly-gully region is very strong, but also a clear seasonal period, the intense evaporation period appeared in summer and autumn, while this time is the rainy season, although soil water can get some of compensation, but the cumulative evaporation is still higher than the total rainfall over the same period. On the crop land is concerned, although water consumption is greater than the same period of precipitation in growing season, soil water part of the deficit, but part of it can be compensated by water storage of soil in winter-spring period of no crop time, yearly pecipitation can meet crop needs. The evapotranspiration law of soil moisture were changed by farmland covered, showing that period for strong evaporation was in advance, evapotranspiration increase, that is excessive soil moisture were consumpted when increase crop production. To take part of ground cover (plastic film mulch, coverage 60%) is conducive to protect soil moisture environment, while taking full coverage (combined coverage and straw mulch, coverage 100%) are conducive to the efficient use of soil moisture. Precipitation pattern take a great impact on the farmland evapotranspiration of one year, overall trend is evapotranspiration volume less than or equal annual precipitation volume in drought years and wet years, and it is greater than or close to annual precipitation volume in normal years. Evapotranspiration volume of crop land is less than the control bare ground in normal years, and it is more than bare ground in wet years; it is more different in drought years: combined coverage and plastic film mulch measures are higher than the control, straw mulch and conventional cultivation is less than control; coverage measures can show their respective performance of cover effectiveness in drought years, as well as little effect in normal and wet years. Water-retention effect of straw mulch is the best in drought years, that of combined coverage is better than others in normal and wet years. The inhibitory effect order of different cover measures on the inter-crop soil evaporation were as follows: combined coverage > straw mulch > plastic film coverage > no coverage. In whole growth period, the combined cover measures can reduce invalid evaporation of bare soil surface 38%, followed by straw mulch measures 28.4% compared with the control, plastic film cover measures decreased by 3.6% compared with the control.(3) Influence of precipitation on soil water use efficiency are far beyond the role of ground cover measures, if the rainfall factor does not take into account, influence of different ground cover measures on soil water use efficiency are very different in the same precipitation year, compared with conventional tillage, three kinds of coverage measures are able to significantly improve the soil water use efficiency in drought years and wet years, water use efficiency of the other two kinds of coverage measures, excepting straw mulch, are lower than conventional tillage in a normal year. To take effective measures for ground cover can significantly improve the utilization efficiency of soil moisture, but its influence varies in different precipitation years. Under normal circumstances, the measures of straw mulch can improve soil water use efficiency, combined coverage measures can better play to their strengths in drought year and the year of high rainfall relatively, the effect is more obvious.(4) Comprehensive evaluation results that use TOPSIS method show that, among 5 measures of agro-technology, comprehensive water efficiency of combined coverage measures is the best, followed by no-tillage straw mulch measures, while no crop land year after year show the worst performance of comprehensive water efficiency, so ranks after the traditional farming measures because of no yield effect. The measures of plastic film mulch which large-scale to promote the use currently in agricultural production, because of its ease of use, yield-increase efficiency significantly, widely recognized at home and abroad, but a comprehensive analysis result shows that the integrated water efficiency are not better than straw mulch.(5) The measures of double materials coverage combined with groove ridge is a special agricultural measures of soil and water conservation, which is organically combined by two kinds of measures of plastic film mulch and straw mulch through the ridge cultivation techniques; in addition to a ridge for planting a series of advantages, in addition to have a series of advantages of the ridge cultivation, it also has both advantages of plastic film mulch and straw mulch, there is its unique advantages.
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